Abstract : The optical properties of the photochromic 1,2-bis(2-methyl-5-((4-mercaptophenyl)ethynyl)-furan-3-yl)perfluorocyclopentene (YnPhT) covalently attached to gold nanoparticles (AuNP) (d = 17 ± 1 nm) were studied in air at ambient conditions. The reversible ring-opening/closing photochromic reactions of molecules attached on AuNP surface can occur under similar light irradiation conditions as observed for free molecules in ethanolic solution. An unexpected blue shift of the local surface plasmon resonance band (LSPR) of AuNP covered by photochromic molecules was observed after UV light irradiation. A reverse red shift of LSPR was observed when the AuNP are illuminated by visible light. Moreover, increased amplitude of the LSPR was observed for AuNP covered with molecules in the closed-ring state. These observations are discussed in view of molecule − AuNP interactions. These interactions decelerate the kinetics of the ring-closing reaction of YnPhT on AuNP surfaces under UV light irradiation.